Thermally insulating articles are well known in the art which comprise a laminated structure of thermal insulation and a flexible jacket with the insulation and jacket being directly adhesively adhered to each other by means of a hot-melt adhesive. One such type of article is pipe insulation, which includes an inner layer of thermal insulation, in the form of a hollow cylindrical member of insulation, usually slitted and opened at one end and usually hinged at the other to facilitate its positioning around pipe for insulation purposes. The thermal insulation typically comprises an inorganic fiber such as, for example, glass or mineral fiber, and a binder, which thermally sets the fibers together with the binder typically being a phenol formaldehyde. Disposed externally of the thermal insulation, and adhesively secured thereto, is a flexible jacket of single-piece construction, which jacket includes an inwardly disposed vapor barrier, typically a metal foil such as, for example, aluminum foil, and an externally disposed paper material. In many instances, the jacket will also include a glass reinforcement, for example, glass scrim, intermediate the vapor barrier, and paper. The jacket is adhesively secured to the thermal insulation by means of a hot-melt adhesive, and the jacket typically employs a pressure sensitive adhesive, which allows for overlapping of longitudinal end portions of the jacket, and by means of the pressure sensitive adhesive allowing for the securing of overlapping portions of the inner surface of one end to the outer portion of an opposite end of the jacket, whereby the pipe insulation can be mounted and secured about the pipe which it is intended to insulate. Such articles are exemplified in U.S. Pat. No. 4,022,248.
In the past, polypropylene has been used as the hot-melt adhesive, but it is generally a relatively expensive material, and there is a need in the art to provide for a more economical hot-melt adhesive, which has all of the needed properties to allow its use in producing the above described thermally insulating articles.
Thus, in accordance with one aspect of the present invention, there is provided an improved hot-melt adhesive especially adapted for use in forming pipe insulation, which adhesive consists essentially of an asphaltene-enriched asphalt, an ethylene-vinyl acetate copolymer and an oxidized microcrystalline petroleum wax.
In another aspect, the present invention provides a lower cost hot-melt adhesive, especially suitable for applications in colder temperatures, which is preferably free from polypropylene and which consists essentially of a propane-washed asphalt, an ethylene-vinyl acetate copolymer and a compatible wax selected from the group consisting essentially of oxidized microcrystalline petroleum wax and non-oxidized waxes, such as paraffin wax, non-oxidized microcrystalline wax, soft polyethylene wax, and hard synthetic crystalline waxes.